1. Field of Invention
The present invention relates to the field of wind power generation. More particularly, the present invention relates to a converter system for wind power generation and a control method thereof.
2. Description of Related Art
With increasingly shortage of energy, increasingly serious energy crisis and the development of power electronic technology and components, wind power generation is continuously developed. With the development of the wind power generation, one single-machine capacity of its related wind power turbine is continuously increased, and thus the capacity of the corresponding converter has to be increased. However, due to various factors, the single-machine capacity of the converter is limited and is hard to be further improved. Thus, those of skills in the art provide the solution of “multi-phase generator & multiple converters” to improve the total capacity of the converter. In particularly, each three-phase winding of the multi-phase generator is connected in series to a back-to-back converter. The back-to-back converter includes a generator-side converter and a grid-side converter. For this solution, since the number of the back-to-back converter is increased, so that the total capacity of the converter can be improved.
Currently, for the solutions mentioned above, the converter is generally controlled through the following two methods:
1) performing control by using a single generator-side controller, wherein specifically, the samples of multiple generator-side converters are all transferred to the same generator-side controller, i.e., all the converters are controlled through only one generator-side controller; and
2) individually controlling the parallel connected converters without circulation current control, wherein specifically, each three-phase winding (every three phases) of the multi-phase generator is individually controlled by a controller, but if the leakage inductance of the generator is relatively small, this control method cannot be implemented.
However, for the method 1), since only one controller is used to control multiple converters, the sampling path and the driving path of the controller is complex and is not easy to be implemented; and for the method 2), since there is no circulation current control, the controlling effect is not good, and especially when the leakage inductance of the multi-phase generator is relatively small, the control method cannot be implemented.
In view of this, many in the industry are endeavoring to find ways in which to design a converter system and a control method thereof for the multi-phase generator to control the converter system, so that the multi-phase generator can be controlled stably and current sharing can be realized among each converter.